Simplex and duplex telegraph system



June 17, 1941., i A. z. SMITH SIMPLEX AND DUPLEX TELEGRAPH SYSTEM Filed Jan. 21, 1939 mm n., MM m W5 m mz A u hm w70 Lm 7 m n E 7 MV QNBMWNH xi Y, B .Imwfl JSNTJTIIRIIJ h 5+ I @wl www@ mv d w Patented June 17, 1941 U TED STAT S OFFICE 'SIMPLEX AND DUPLEX TELEGRAPH SYSTEM Arthur Z. Smith, Riverhead, N. Y., assigner to Radio Corporation of America, a corporation of i Delaware This invention relates to telegraphy, both wire and radio. More specically, it relates to circuit arrangements for interconnecting simplex telegraph to duplex telegraph loops without use of electromagnetic or other kinds of mechanical relays. In prior art circuits, as far as I am aware, it has been the practice to use electromagnetic relays, operated in response to the signal currents, to switch the circuits from simplex to duplex operation and vice versa. Considerable time is required for adjustment and maintenance of these relays and elimination of the relays is desirable.

One of the objects of my invention is to accomplish the change fronnsimplex to duplex operation without any contact relays whatever.

Another object is to accomplish the shift from simplex to duplex by means of electron tube circuits.

Other objects will appear in the following specication, reference being had to the drawing in which:

Fig. 1 is one form of the invention.

Fig. 2 is a second form of accomplishing the desired results.

Referring to Fig. 1, when transmission and reception in simplex operation is to be had, switch I will be thrown to the left into engagement with contacts 2 and 3 and when the circuit is to be operated on duplex, the switch I will be thrown to the right into engagement with contacts 4 and 5. Simplex printer 6 is shown permanently connected in circuit but duplex printer 'I will have its plug 8 inserted in jack 9 only when the switch I is in engagement with contacts 4 and 5 for duplex operation.

The printers are shown only generally at 6 and 'I and they may be of any type. Also, the invention may be used with other forms of telegraph sending and receiving devices such as Morse keys and Sounders, for example.

Merely for explanatory purposes, I have diagrammatically illustrated the devices 6 and I as teletype ve-unit type bar tape printers which are well known in the art. Each of these teletypes, as is customary, is arranged for printing messages and for transmitting messages to a similar instrument at some other station.

For radio operation, the signals may be received in antenna l, after which they may be amplified at radio frequency, detected and amplied at audio frequency as usual. Devices for accomplishing this purpose are Well known in the art and hence they are indicated only generally by reference character II.

It is usual, though not essential, to operate a tone keyer I2 by the rectified Signals from II as is described, for example, in the patent to Beverage and Peterson No. 1,874,866, though the exact form there described need not necessarily be used. Since this is an old and well known form of apparatus it need not be further described. The tone signals are transmitted usually to a distance from the receiving stationl where they are rectified as generally indicated at I3. The rectified signal voltage is then applied across resistance i4. One terminal of this resistance is connected to the unipotential cathodes I5, I6, and, as indicated, this will be connected to the minus terminal of the direct current supply generally indicated at 2 I.

In this particular embodiment of my invention, I have arranged for utilization of reverse keying, that is, there is no potential in resistance I4 for signal marks but there is potential across that resistance for signal spaces. This reversal of signals may take place at the distant transmitter, in the receiving apparatus Il, or at any other desired place. f

The rectier I3 is so connected to resistance I4 that terminal I'I will be negative and terminal I3 positive insofar as the tone signal voltage is concerned. Both of the grids are connected to the terminal I1 of resistance I4 and the circuit to the cathodes is completed at terminal I8. When no signal currents are received in resistance I4, that is, during the normal mark of the signal, plate current flows under a plate potential of 250 volts derived from battery I'I, though of course the battery voltages are given merely as suitable values. This is applied across negative terminal 2l and relatively positive ground terminal 22.

For sending purposes, it is desirable, though, of course, not absolutely essential, to put a tone on signals sent out by the keyboard transmitter. This is accomplished by generator 26. In simplex operation the tone is applied in the common plate circuit through transformer secondary 2l and in duplex operation through transformer 28.

The cathode of l tube 29 is connected to a point in the bias potentiometer generally indicated at 3 i. This consists of resistances 32 and 33 between which the cathode of tube 29 is connected and resistances 34 and 35. Resistance 34 in combination with resistance 35 or printer 'I biases the cathode of tube 3B. When the plug 8 of printer 'I is removed from jack 9, resistances 34 and 35 are connected together at contact 38 but when the plug 8 is inserted the tip separates the con- 55 tact points and the resistance of printer 'I is substituted in place of resistance 35. Resistances 32 and 34 may have, for example, a value of 1500 ohms and resistances 33 and 35 may have the same value as the printer which usually is of the order of 100 ohms.

The pl'ates of tubes 29 and 30 are connected in opposition through primary 39, as in push pull circuits, to the positive terminal +V. The secondary 40 of the plate transformer is connected to the transmitting apparatus 4I for radiation of signals from antenna 42. Of course in wire teleggraphy line conductors would be substituted for the radio apparatus in an obvious manner.

Simplex operation will now be described. Switch I will be thrown to the left-hand position, as shown on the drawing, and plug 8 of printer 1 will be removed from jack 9. In simplex operation printer 6 will receive from antenna I and transmit from antenna 42.

The tubes I9 and 20 draw current during the mark part of the reversed signals. They draw no current during the space part of the signal because the signal drop in resistance I4 makes the grids sufficiently negative to block the tubes. It will thus be seen that the circuit arrangement changes the signals so they are non-reversed in the plate circuit of tubes I9 and 20 and they thus can operate the printer 6 in the usual way.

Since the operation of the printer is well known,

-and specifically forms no part of my invention, its

detail operation need not be described.

In reception the potential Variations in the plate circuit due to the mark and space parts of the signal, will not cause re-radiation of the signals through antenna 42 as the grids of keying tubes 29 and 30 are equally affected since the value of resistance 23 is the same as that of printer 6.

In transmitting when the contacts of printer 6 open the circuit for the space parts of the code character, the action is diierent. During this time the drop in resistance 23 is unchanged while the tone potential drop in the printer is eliminated. The grid of tube 29 thus receives the tone potential variations while tube 36 does not. Hence signals will be sent into `the output circuit to the transmitting apparatus 4I and radiated by the antenna 42. In this circuit arrangement signals are transmitted during the space parts of the signal code unit and not during the mark part of the code unit. In other words, the circuit arrangement reverses the signals, thus enabling the distant receiving station to use the printer `receiving circuits already described.

I prefer to connect .the plate 25 to ground through high resistance 43, as shown, so that the grid of keying tube 39 is not floating when then printer contacts are open. This resistance may -have various high values but 100,000 ohms is satisfactory.

For duplex work the switch will be thrown to the right. In this position the printer 6 will be used only for receiving and printer 1 will be .plugged into the circuit for transmitting only.

i In transmittingwhen the circuit in printer 1 is :closed (marking part of code unit) no signal will be transmitted because the tone potentials from transformer 28 will balance out in the output 49 because the grids of tubes 29 and 30 are simultaneously aiected When the circuit of printer'i is open the grids ,are not equally affected :because the normal grid cathode circuit of tube 30 then is open at the yprinter contacts and the grid-cathode circuit of this 'tube is extended through potentiometer rein an equal degree.`

`tube '48 and no `radiation takes place.

sistances 32, 33 and 34. There is no bias potential at this time on resistance 34 due to the opening of the printer contacts but full negative potential of 125 volts exists across resistances 32 and 33. This blocks tube 30 or so reduces its output that the tube circuit is unbalanced and a tone signal is transmitted through the output transformer of the keying tubes. Signals are thus transmitted for the spaces, This again sends out reversed signals though, of course, the signals could be re-reversed before radiation, if desired.

It will be clear from the foregoing description that the circuits of Fig. 1 permit full simplex or duplex operation without the usual relay contactors.

In Fig. 2 I have shown a circuit for changing from simplex to duplex without relay contactors with normal or unreversed signals. The signals after rectication in I3 develop potentials across resistance V44, any desired part of which is applied to the input circuit of tube 45. The negative grid bias in resistance 48 is suiciently high to block the tube when no signal potential exists in resistance 44. No potentials exist in resistance 44 when spaces" are being sent but they do exist when marks are being sent. Under these conditions printer 6 prints the messages received in the normal way.

When a signal mark is received in printer 6 there will be a drop of about seven volts across resistance 41 and this will be applied to the grid of keying tube 48 which is supplying continuous tone in the plate circuit from tone generator 26 when the printer is on stop This tube operates as a class A amplifier. 'I'he seven volts drop in resistance 41 is, however, too low to appreciably affect the grid modulations of tube 48 as it is of low mu and requires about 40 volt negative bias for Class A operation. The received signal is therefore not appreciably re-radiated.

When printer 6 is used for simplex transmission and the printer contacts are opened (signal space) the potential drop in resistance 41 is very much higher than the printer drop as its resistance is in the neighborhood of 10,000 ohms. This voltage applied to the grid of keying tube 48 is sufficient to block it and no tone modulated current flows in the output circuit. Simplex transmission as well as reception is therefore readily carried on with this circuit arrangement without mechanical contact devices.

For duplex operation printer 1 will be plugged into the jack. This will isolate printer 6 from the transmitter circuit. It will then be used exclusively for reception. This also connects resistance `potentiometer 49 in circuit to provide the proper voltage for operating the printer and suitable bias for keying the tube 48. The potentiometer 50 furnishes the plate Voltage and grid bias for the tube 48. When the printer contact is opened resistance arm 5I of the potentiometer places a high negative bias in the grid circuit of tube 46 as `it is a high resistance. This blocks When the printer contact is closed a tone modulated signal is transmitted by tube 48 as high resistance 49 is then shunted by the low printer resistance of ohms.

Obviously the tube supply voltages can be obtained from a common battery source and the separate sources indicated are not requisites of the invention.

In case one desires to use the circuit of Fig. 2 with reversed signals, the polarities of the bias voltages in the grid circuits of tubes 45 and 48 would be reversed so the tubes would normally conduct current and would be blocked by the signal voltage as in Fig. 1. This change to reception and keying of reversed signals will be apparent from the description of Fig. 1 and need not be further described.

Having described my invention, what I claim is:

1. In telegraph systems, a signal source, a telegraph sender-receiver and an impedance joined in a series circuit across the signal source, a source of alternating potential having one terminal connected to the junction point between the senderreceiver and the impedance, a pair of electron tubes, the other terminal of said source of alternating potential being connected to the cathodes of said tubes, the input electrode of one tube being connected to a point in said impedance and the input electrode of the other tube being connected to a point in said printer, said points having substantially equal alternating potential and the output circuits of said tubes being connected in opposition.

2. In telegraph systems, a pair of electron tubes, a signal source connected to the input electrodes of said tubes, a sending-receiving device and an impedance device constituting a series circuit connected across the output electrodes of said tubes, a source of potential connected between the junction point of said devices and the cathodes of the tubesy a second pair of electron tubes, means for impressing the potential drop of said series circuit across the input electrodes of the second mentioned tubes, and for impressing the potential drop of one of said devices in the input circuit of one of the second mentioned tubes and the potential drop of the other of said devices in the input circuit of the other of said second mentioned tubes and a utilization circuit connected across the anodes of the second mentioned tubes.

3. In telegraph systems, a pair of electron tubes, a signal source connected to the input electrodes of said tubes, a sending-receiving device and an impedance device constituting a series circuit connected across the output electrodes of said tubes, a source of alternating potential connected between the junction point of said devices and the cathodes of the tubes, a second pair of electron tubes, means for impressing the potential drop of said series circuit across the input electrodes of the second mentioned tubes, and for impressing the potential drop of one of said devices in the input circuit of one of the second mentioned tubes and the potential drop of the other of said devices in the input circuit of the other of said tubes and a utilization circuit connected across the anodes of the second mentioned tubes.

4. In telegraph systems, a pair of electron tubes, a signal source connected to the input electrodes of said tubes, a sending-receiving device and a resistance constituting a series circuit connected across the output electrodes of said tubes, a source of alternating potential connected between the junction point of said device and said resistance and the cathodes of the tubes, a second pair of electron tubes, means for connecting a pair of equi-potential points of said series circuit to the input electrodes of the second mentioned tubes, a connection'from the cathodes of the second mentioned tubes to said junction point, and a utilization circuit connected across the anodes of the second mentioned tubes.

5. In telegraph systems, a pair of electron tubes, a signal source connected to the input electrodes of said tubes, a sending-receiving printer and a resistance connected in a series circuit across the output electrodes of said tubes, a second pair of electron tubes, a source of alterhating potential connected to the junction terminal of the printer with said resistance and the cathodes of all of said tubes, a connection between the input electrodes of one of the second mentioned tubes and the other terminal of the printer, a connection between the input electrode of the other of the second mentioned tubes and the other terminal of the resistance, a transformer connected across the anodes of the second mentioned tubes, and a source of potential connected between the cathodes of the second mentioned tubes and the midpoint of said transformer.

6. In telegraph systems, a signal source, an electron tube having its input electrode and cathode connected to said signal source, a telegraph sending-receiving device having means for opening and closing its circuit connected between the anode and cathode of said tube, a resistor connected in shunt to said device having a high resistance in comparison to that of the device whereby it is substantially short circuited by the device when its circuit is closed, a second electron tube having its input circuit connected to receive a voltage drop in said device.

7. In telegraph systems, a signal source, an electron tube having its input electrode and cathode connected to said signal source, a telegraph sending and receiving printer having contacts for opening and closing the circuit connected between the anode and cathode of said tube, a source of potential connected in the circuit between the anode and cathode, a resistance, high in respect to the resistance of printer, connected in shunt to said printer, a second electron tube having its input circuit connected to receive a voltage drop in said resistance, and a transmitting output circuit connected between the anode and cathode of the second mentioned tube.

8. In telegraph systems, a source of incoming signals, a sender-printer and a'resistance connected in series across said source, transmitting apparatus, a relay connected across said senderprinter, a relay connected across said resistance, means for connecting said relays in opposition to said transmitting apparatus, and a source of potential applied in parallel to said resistance and sender-printer.

9. In telegraph systems, a source of incoming signals, a sender-printer and a resistance connected across said source, transmitting apparatus, a source of potential applied in parallel to said resistance and sender-printer, a relay connected to receive potential from said resistance, and means for connecting said relay to said transmitting apparatus.

ARTHUR Z. SMITH. 

